This invention pertains to corrosion resistant water dispersed polymers, and more particularly to phosphorus containing emulsion or solution polymerized polymers suitable for use as paint binder in protective surface coating systems.
Latex polymer systems containing phosphorus additives are suggested in U.S. Pat. No. 4,169,086 where the use of organic phosphates and phosphonates are suggested as buffers in a latex polymerization. Phosphated monomers are disclosed in U.S. Pat. No. 3,686,371 as well as the Journal of Polymer Science, Vol. 1, pages 3343-3356 (1963). Water based coating compostions for use as an interior coating for metal containers are suggested in U.S. Pat. No. 3,991,216 wherein the polymer comprises an interpolymer of polymerized acrylamide monomer, carboxylic monomers and other ethylenically unsaturated monomers. Commonly assigned copending application Ser. No. 468,364 filed Feb. 22, l983 discloses a self-curing water dispersed emulsion polymerized polymer containing both alkyl acrylamide monomer and reactive functional monomer in combination with an epoxy-acrylic copolymer and a phosphated polymer. Other prior art patents such as U.S. Pat. No. 4,237,241, U.S. Pat. No. 4,181,784 and U.S. Pat. No. 4,181,785 suggest that cross linking reactions between polymers containing hydroxyl functionality and amine type crosslinkers are catalyzed by certain hydroxy organophosphate esters.
It now has been found that an emulsion polymerized polymer containing copolymerized phosphoric monomer in combination with an alkylol acrylamide monomer provides a substantially improved self-curing phosphate containing polymer exhibiting improved corrosion resistance and similar desirable film integrity properties. In accordance with this invention, an hydroxy phosphate monomer is first prepared from glycol or epoxy resin which in turn is emulsion or solution copolymerized with alkylol acrylamide monomer, functional monomer, and other monomers to produce the self-curing phosphate polymer. The copolymerized hydroxy phosphate is adapted to internally crosslink with the functional monomer and may further function as a catalyst for subsequent crosslinking with an external crosslinker such as melamine. Inclusion of the hydroxy phosphate ester monomer promotes reaction between polymeric hydroxyl groups and crosslinkers, and may also participate in these crosslinking reactions through the hydroxyl functionality adjacent to the phosphate ester. Improved crosslinking efficiency and improved incorporation of polymer catalyst and crosslinker into the crosslinked network is thereby achieved. Less external crosslinker is required to provide high molecular weight cured films, which can be achieved at much lower curing temperatures. Thus, advantages of this invention include improved crosslinking efficiency resulting in sufficient cure at reduced levels of copolymerized and external crosslinkers as well as lower bake temperatures. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples set forth hereinafter.